1. Field of the Invention
The present invention relates generally to gas injection systems for processing reactors.
2. Discussion of the Background
The inventors have identified a problem with conventional processing reactors that is solved by the present invention. The inventors have determined that in conventional processing reactors using conventional gas injections systems particulate contamination can occur on a substrate being processed due to particulate deposition upon the substrate during process initialization. For example, when gas flow is initialized to start a process, a mass flow controller is generally opened to allow a precise flow rate of gas(es) into the vacuum chamber, hence exposing a high pressure region (e.g., 10's of psi) upstream of the controller to a low pressure region (e.g., 100's of mTorr) downstream of the controller and within the vacuum chamber. When this occurs compression waves will travel through plumbing of the gas injection system to the vacuum chamber, while expansion waves will propagate backward towards the high pressure region. The compression waves will travel at approximately an average speed of sound between the two gas pressure regions. The compression waves will exhibit strong gradients in flow properties. The locally intense flow structures caused by the compression waves could cause removal of particulate material from surfaces of the gas injection system, and transporting of the particulate material onto the substrate through an inject plate in the chamber. In other words, the substrate could be exposed to the gas injection system “sneezing” upon it.
The inventors have determined that the initial transients associated with the sudden flow of gas from a region of high pressure to a region of low pressure can cause the generation of gas entrained particles due to the sharp flow gradients developed under a sudden expansion. Also, due to the presence of the substrate below the inject electrode, the unwanted particles may be deposited upon the substrate causing reduced process yield. The problem is further exacerbated in systems requiring high pressure gas injection. In an effort to eliminate or minimize these potential sources of contamination, the inventors have constructed an apparatus and method as described in detail below.